Front wheel drive vehicles having independent front wheel suspension use a pair of half shaft assemblies to transmit power between the vehicle's engine and the front wheels.
Typically these half shaft assemblies comprise a fixed constant velocity joint (CV joint) at one end and a plunging CV joint at the opposite end. These joints are connected by an interconnecting shaft. The fixed joint is typically positioned at the wheel side of the vehicle. These joints are designed to allow a large angle (45°-50°) of operation. The fixed joints allow the front wheels to be steered in order for the vehicle to negotiate corners.
The center of angulation of a plunging CV joint is typically positioned at the inner end of the half shaft, which is connected to a transmission or transaxle of the vehicle. This plunging CV joint is typically designed for smaller angles of articulation (20°-25″). The center of angulation of the plunging CV join is not axially fixed, but is allowed to move axially (plunge) along the axial center line of the outer member of the joint. This capability of articulation and plunge movement allow the joint to transmit power while at the same time accommodating suspension and engine movement.
A tripod joint is one design of a plunging constant velocity joint. A tripod joint comprises an outer member with three circumferentially spaced longitudinal chambers. Disposed within these chambers is a spider assembly. The spider assembly comprises a tripod member with three circumferentially spaced radially extending trunnions. Each trunnion is surrounded by a roller. Needle bearings are journaled between the roller and the trunnion. This permits free rolling of the roller on the trunnion. The outer surface of the roller is in contact with the sides of the longitudinal chambers of the outer member.
When the tripod joint is at a 0° angle, the plunging effect is relatively low. The roller rolls against the longitudinal chamber of the outer member and rotates on the trunnion of the inner member using the plurality of needle bearings.
When the tripod joint is operated at an angle, the tripod roller is not free to roll along the track because the plane of the tripod roller is skewed relative to the plane of the outer member's chamber. This skewed relationship causes the roller to both roll and slide along the longitudinal chamber. As the joint angle increases, the amount of sliding also increases.
A torque load on the tripod joint during operation at an angle larger than 0° produces a secondary moment in a radial direction with respect to the axis of rotation of the joint. This secondary torque has the tendency to change the angle of operation of the tripod joint. Therefore, an appropriate support should be provided to reduce the effect of the secondary moment.
A link shaft extends from the inner end of each half shaft to connect the half shafts to the differential coupled to the transmission. The link shaft can be a separate component or integrated with the outer member of the plunging CV joint. Ideally, the distance between the fixed CV Joint and the plunging CV Joint is identical between the right wheel half shaft assembly and the left wheel half shaft assembly. However, in vehicles with front wheel drive and a transversely mounted engine, the output of the transmission is arranged off-center, resulting in link shafts of the right wheel and left wheel having different lengths.